材料期刊网

采用基于密度泛函理论Castep和Dmol程序软件包,计算了ZA62镁合金中AB_2型金属间化合物MgZn_2,Mg_2Sn和MgCu_2的结构稳定性、弹性性能与电子结构.合金形成热和结合能的计算结果显示:Mg_2Sn具有最强的合金化形成能力,而MgCu_2结构最稳定;体模量(B)、弹性各向异性系数(A)、Young's模量(E)、剪切模量(G)和Poisson比(v)的计算结果表明:MgZn_2和MgCu_2为延性相,而Mg_2Sn为脆性相,MgZn_2的塑性最好;采用弹性常数、体模量和结合能的经验公式计算金属间化合物的熔点,实验值均在采用弹性常数(±300 K)和体模量(±500 K)计算熔点预测的范围内,采用弹性常数比采用体模量和结合能预测熔点的平均相对误差小,其中采用弹性常数计算Mg_2Sn的熔点与对应的实验值十分接近,相对误差仅为0.31%.不同温度下热力学性质的计算结果表明,在298-573 K温度范围内,MgCu_2的Gibbs自由能始终最小,其结构热稳定性最好,结构稳定性的强弱顺序并不随温度的升高而消失;而对MgZn_2和Mg_2Sn,以475 K为临界,结构稳定性的强弱顺序随温度的升高发生了变化;态密度和Mulliken电子占据数的计算结果表明:MgCu_2结构最稳定的原因主要在于体系在Fermi能级以下区域成键电子存在强烈的离子键作用.

Structural stabilities, elastic properties and electronic structures of Mg_2Sn, Mg_2Zn_2and MgCu_2in ZA62 magnesium alloy have been determined from first-principles calculations by using Castep and Dmol program based on the density functional theory. The calculated heats of formation and cohesive energies showed that Mg_2Sn has the strongest alloying ability and MgCu_2the highest structural stability. The calculated bulk moduli (B), anisotropy values (A), Young's moduli (E), shear moduli (G) and Poisson ratio (v) showed that MgZn_2and MgCu_2both are ductile, on the contrary, Mg_2Sn is brittle, and among the three phases MgZn_2is a phase with the best plasticity. Their tested melting temperatures are within the ranges calculated from elastic constants (±300 K) and bulk moduli (±500 K), the estimated values from elastic constant have the smallest average relative error, the calculated melting temperature of Mg2Sn phase is in well agreement with the experimental one and the error relative to the experiment result is about 0.31%. MgCu_2has higher melting temperature, I.e.better structural stability among the three compounds. The calculations of thermodynamic properties show that the Gibbs free energy of MgCu_2is also the smallest within 298-573 K range, indicating the structural stability of MgCu_2does not change with the elevated temperature. The calculations of the density of states (DOS) and Mulliken electronic populations showed that the reason of MgCu_2having highest structural stability in ZA62 magnesium alloy attributes to MgCu_2phase having more ionic bonds below Fermi level compared with those of Mg_2Sn and MgZn_2phases.